Surface treatment method, shower head, processing container, and processing apparatus using them

ABSTRACT

The method of the present invention includes: a first blasting step of carrying out blasting of the surface of a metal base material, such as a shower head or a processing container, by using a blasting material composed of a non-sublimable material (e.g. alumina); and a second blasting step of carrying out blasting of the surface of the metal base material, which has undergone the first blasting step, by using a blasting material composed of a sublimable material (e.g. dry ice). The first blasting step properly roughens the surface of the metal base material so that a film, which adheres to the surface during film-forming processing, hardly peels off. In addition, the second blasting step almost fully removes the residual non-sublimable blasting material adhering to the surface of the metal base material, thereby preventing the generation of particles deriving from the residual non-sublimable blasting material falling off the metal base material.

TECHNICAL FIELD

The present invention relates to a processing apparatus for carrying out predetermined processing of a processing object such as a semiconductor wafer, relates to a shower head and a processing container for use in the apparatus, and relates to a surface treatment method.

BACKGROUND ART

In the manufacturing of a semiconductor device such as a semiconductor integrated circuit, a semiconductor wafer, e.g. comprised of a silicon substrate, is generally subjected to various types of processing, such as film-forming processing, etching, annealing, diffusion processing, etc., carried out repeatedly.

In a film-forming apparatus for carrying out film-forming processing, one of the various types of processing, a semiconductor wafer is placed on a stage provided in an evacuable processing container, and a predetermined film-forming gas is allowed to flow into the processing container from a shower head, provided in a ceiling portion and facing the stage, so that a film is formed on the wafer which is kept at a predetermined temperature (see e.g. Japanese Patent Laid-Open Publications Nos. H11-186197 and 2004-232080).

The film deposits not only on the surface of the semiconductor wafer, but unavoidably deposits as an unnecessary attached film also on the interior surface of the processing container, the surface of the shower head, etc. In order to prevent the unnecessary attached film from falling off and generating particles which can lower the product yield, cleaning to remove the unnecessary film is conventionally carried out either periodically or as needed.

It is also conventional practice to carry out processing to enhance the adhesion of such an unnecessary attached film so that the film will not fall off easily. Japanese Patent Laid-Open Publication No. 2002-115068 discloses a technique which involves thermally spraying alumina onto the surface of a shower head to roughen (produce micro irregularities) the surface so that by the anchor effect, an attached film can be prevented from peeling off the surface.

The JP 2002-115068 document also describes that a technique has also been studied which comprises roughening the surface of a shower head by alumina blasting. The document describes that the surface roughening by blasting can reduce the generation of particles to some extent as compared to the case where the surface of the shower head is a mechanically machined surface. The particle generation reducing effect of blasting, however, can hardly be deemed to fully satisfy recent particle level requirements. The JP 2002-115068 document describes that the particle generation decreasing effect of alumina blasting is inferior to the particle generation reducing effect of alumina spraying.

Alumina spraying, however, can hardly be deemed as the best method for surface roughening. Alumina spraying entails increased cost of the product. In addition, sprayed alumina particles can fall off and become particles. It is, therefore, preferred if an improvement in blasting enables fully satisfactory decrease of particles.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above situation. It is therefore an object of the present invention to provide a surface treatment method characterized by an improved blasting technique capable of reducing the generation of particles. It is also an object of the present invention to provide parts to which the surface treatment method has been applied and a processing apparatus provided with the parts.

It has been found through studies by the present inventors that a considerable amount of alumina particles (residual blasting material) remain on a member (e.g. shower head) which has undergone alumina blasting, and the residual blasting material falls off and becomes particles due to thermal expansion of the base material (shower head material) caused by a rise in the temperature during the operation of the apparatus. Cleaning, such as ultrasonic cleaning or brush cleaning, is generally carried out after alumina blasting. Such cleaning, however, has been found to be inadequate to remove particles sticking in the base material. The present inventors have found that by carrying out second blasting of a base material with particles of a sublimable material, especially dry ice particles, as a blasting material after carrying out first blasting of the base material with a rigid non-sublimable material, such as alumina particles, the residual blasting material, remaining on the base material after the first blasting, can be efficiently removed, thereby significantly decreasing particles deriving from the residual blasting material. Conveniently, the blasting material used in the second blasting sublimates and disappears and thus will not remain as a residue on the surface of the base material after the second blasting. Further, it would appear the second blasting, carried out by using a blasting material which is generally softer than a blasting material for use in the first blasting, can moderate the sharpness of surface micro protrusions as described in the JP 2002-115068 document without significantly losing the surface roughness obtained by the first blasting. The generation of particles, caused by peeling of an attached film from the base material, can therefore be prevented. Thus, it would appear that particles can be significantly decreased by the synergistic effect of the combination of the first blasting and the second blasting.

The present invention has been made based on the above findings. Thus, the present invention provides a surface treatment method for performing predetermined surface treatment of a metal base material, comprising: a first blasting step of carrying out blasting of the surface of the metal base material by using a non-sublimable blasting material composed of a non-sublimable material; and a second blasting step of carrying out blasting of the surface of the metal base material, which has undergone the first blasting step, by using a sublimable blasting material composed of a sublimable material.

The surface treatment method may further comprise a cleaning step of cleaning the surface of the metal base material which has undergone the second blasting step.

The non-sublimable blasting material may be a material selected from the group consisting of a ceramic material, a resin, a metal oxide and quartz. In this case, the ceramic material may be selected from alumina (Al₂O₃), aluminum nitride (AlN), silicon nitride (SiN) and silicon carbide (SiC). The metal oxide may be ZrO₂ or TiO₂.

The sublimable blasting material may be dry ice.

The metal base material may be a shower head for use in a processing apparatus for carrying out predetermined processing of a processing object. Alternatively, the metal base material may be a processing container for use in a processing apparatus for carrying out predetermined processing of a processing object.

The first and second blasting steps may be carried out only on a selected area of the surface of the metal base material.

In a preferred embodiment, the metal base material is a shower head for use in a processing apparatus for carrying out predetermined processing of a processing object, and the first and second blasting steps are selectively carried out only on an area around each of gas jet holes provided in the shower head.

The present invention also provides a shower head and a processing container which have undergone the above-described surface treatment.

The present invention also provides a processing apparatus comprising: a processing container which has undergone the above-described surface treatment; a shower head which has undergone the above-described surface treatment; a stage, for placing a processing object thereon, provided in the processing container; and an exhaust system for evacuating the atmosphere in the processing container.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an exemplary processing apparatus using a metal base material which has undergone surface treatment according to the present invention;

FIGS. 2A through 2C are diagrams showing the flow of the surface treatment method of the present invention;

FIG. 3 is a flow chart showing the flow of the surface treatment method of the present invention;

FIG. 4 shows electron photomicrographs for illustration of the evaluation of blasting with a sublimable blasting material;

FIG. 5 is a table for illustration of the evaluation of particles in a processing apparatus using a shower head which has been processed by the method of the present invention or a shower head which has been processed by a conventional method; and

FIGS. 6A and 6B are diagrams illustrating a variation of the method of the present invention.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described in detail with reference to the drawings. A description is first given of a metal base material which has undergone surface treatment according to the present invention, and a processing apparatus provided with the metal base material. In the below-described illustrative embodiments, the metal base material is a shower head or a processing container. Surface treatment according to the present invention may be applied to at least one of the two members.

FIG. 1 is a schematic diagram showing an exemplary processing apparatus using a metal base material which has undergone surface treatment according to the present invention. FIGS. 2A through 2C are diagrams showing the flow of the surface treatment method of the present invention. FIG. 3 is a flow chart showing the flow of the surface treatment method of the present invention. A film-forming apparatus for forming a Ti film by using a plasma is herein described as an exemplary processing apparatus; however, the present invention, of course, is not limited to such a film-forming apparatus.

As shown in FIG. 1, the processing apparatus 2 includes a cylindrical processing container 4 of a metal material, such as nickel or a nickel alloy, or aluminum or an aluminum alloy. The processing container 4 is grounded. The processing container 4 is a metal base material whose interior surface has undergone surface treatment according to the present invention. In the processing container 4 is provided a stage 8, e.g. made of a ceramic material such as aluminum nitride, supported on an upright support column 6 extending from the container bottom. A wafer W is placed on the upper surface of the stage 8.

A heating means 10, which is a heater comprised of a molybdenum wire, is embedded in the stage 8 so that the wafer W can be heated to a predetermined temperature. Further, a mesh-like conductive member 12, located above the heating means 10, is embedded in the stage 8. The conductive member 12 is grounded via a not-shown wire and configured to function as a lower electrode (ground electrode) for plasma generation. A high-frequency power for bias may be applied to the lower electrode. Below the stage 8 are provided lifter pins (not shown) which, upon transfer of the wafer W, move upward, and push up the wafer W from below while support it.

An exhaust port 14 is formed in the bottom of the processing container 4. To the exhaust port 14 is connected an exhaust system 16 including a vacuum pump, a pressure regulation valve, etc., so that the atmosphere in the processing container 4 can be evacuated and a predetermined internal pressure can be maintained.

An opening 18, having such a size as to allow passage of the wafer W, is formed in the side wall of the processing container 4. The opening 18 is provided with a gate valve G. The ceiling portion of the processing container 4 is open, and in the opening is airtightly mounted, via an insulating member 20, a gas introduction means, e.g. a shower head 22. The shower head 22 is composed of a metal material, such as nickel or a nickel alloy, or aluminum or an aluminum alloy. The shower head 22 also functions as an upper electrode. A diffusion chamber 24 is formed in the shower head 22.

A large number of gas jet holes 30, communicating with the diffusion chamber 24, are formed in the lower gas jet surface 28 of the shower head 22 so that a desired gas can be introduced into a processing space S in the processing container 4. The shower head 22, especially the lower gas jet surface 28, is a metal base material which has undergone surface treatment according to the present invention.

A gas introduction port 32 is formed in the upper portion of the shower head 22. Predetermined gases, in particular TiCl₄ gas, H₂ gas and Ar gas in this embodiment, are introduced respectively at a controlled flow rate through the gas introduction port 32 into the shower head 22. The gases are diffused in the diffusion chamber 24, and uniformly jetted from the gas jet holes 30 into the processing space S over the wafer W. Instead of the one diffusion chamber, two or more diffusion chambers may be provided depending on the types of gases used. In that case, different gases may be introduced from their respective gas introduction ports, and may be individually jetted into the processing space S.

A feed line 38, in which a matching circuit 34, a high-frequency power source 36 (e.g. having a frequency of 450 kHz) for plasma generation, etc. are interposed, is connected to the shower head 22, so that a plasma can be formed between the shower head 22, serving as an upper electrode, and the stage 8 serving as a lower electrode. A Ti film can be farmed by plasma-assisted CVD on the surface of the wafer W by supplying a processing gas, consisting of TiCl₄, H₂ and Ar, to the processing space S in the processing container 4 and generating a plasma of the processing gas by application of a high-frequency power, and heating the wafer W to a predetermined temperature with the heating means 10.

[Surface Treatment Method]

As described above, the processing container 4 and the shower head 22 of the processing apparatus 2 having the above construction have undergone surface treatment according to the present invention. The surface treatment method will now be described. As shown in FIGS. 2 and 3, the surface treatment method of the present invention is carried out on a metal base material 40 which is either the processing container 4 or the shower head 22.

The surface treatment method comprises: a first blasting step of carrying out blasting of the surface of the metal base material 40 by using a non-sublimable blasting material composed of a non-sublimable material (step S1, see FIG. 2A); and a second blasting step of carrying out blasting of the surface of the metal base material 40, which has undergone the first blasting step, by using a sublimable blasting material composed of a sublimable material (step S2, see FIG. 2B). The “non-sublimable material” herein refers to a material which does not sublimate under the temperature/pressure conditions during or after surface treatment; and the “sublimable material” herein refers to a material which sublimates under the temperature/pressure conditions during or after surface treatment. Preferably, after the second blasting step, a cleaning step of cleaning the surface of the metal base material 40 which has undergone the second blasting step is carried out (step S3, see FIG. 2C).

In the first blasting step, a ceramic material alumina (Al₂O₃), for example, can be used as the non-sublimable material. The first blasting step can be carried out by spraying the blasting material, comprised of fine alumina particles, by means of compressed air using an air blasting machine.

In this case, the blasting material may have a particle size in the range of #220 to #20. The unit “# (mesh)” herein refers to the Tyler unit, indicating the size of particles. When the processing container 4 is used as the metal base material 40, blasting is preferably carried out on the entire interior surface of the processing container 4. When the shower head 22 is used as the metal base material 40, blasting is preferably carried out on the gas jet surface 28 of the shower head 22, and more preferably carried out on the entire area of the surface which is to be exposed to the processing space S.

The surface of the metal base material 40 is approximately uniformly roughened by the first blasting and micro irregularities are formed in the surface. The surface roughness Ra (arithmetic mean roughness defined by JIS B 0601-1994) of the surface of the metal base material 40 is preferably made about 1.0 to 2.0 μm.

The non-sublimable blasting material is not limited to alumina, and can be selected from a ceramic material, a resin, a metal oxide and quartz. The ceramic material can be selected from alumina (Al₂O₃), aluminum nitride (AlN), silicon nitride (SiN) and silicon carbide (SiC). The metal oxide can be selected from ZrO₂ and TiO₂.

In the second blasting step, dry ice, for example, can be used as the sublimable material. The second blasting step can be carried out e.g. by spraying the blasting material, comprised of fine dry ice particles, by means of compressed air using an air blasting machine.

The second blasting is carried out at least on the entire area of the surface which has undergone the first blasting. By carrying out the second blasting, the non-sublimable blasting material, i.e. alumina particles, which adhered to the surface of the metal base material 40 upon the first blasting and hardly fall off the surface, can be almost fully removed.

As described above, after carrying out blasting with alumina particles, it is common practice to carry out cleaning, such as ultrasonic cleaning, to remove the residual particles adhering to the blasted surface. Residual particles, sticking shallowly in the blasted surface, may be removed easily; however, it is difficult to remove residual particles sticking deep in the blasted surface.

According to the method of the present invention, on the other hand, blasting with dry ice is carried out after blasting with alumina. The second blasting can easily remove residual particles, sticking deep in the blasted surface, which cannot be removed by ultrasonic cleaning. Residual particles, sticking very deep in the blasted surface, may not be removed even by the blasting with dry ice. Such residual particles, however, little fall off the surface of the metal base material 40 even when the metal base material 40 is brought to a high temperature upon processing of a wafer, and therefore will not cause the particle problem.

The dry ice blasting material, if it sticks in the surface of the metal base material 40, sublimates at ordinary temperature and pressure, and thus will not remain on the surface of the metal base material 40.

The blasting with dry ice does not significantly change the surface roughness after the blasting with alumina, and can substantially maintain the surface state after alumina blasting. Accordingly, the anchor effect of the irregularities of the base material surface will not be reduced, and thus peeling of a film adhering to the surface can be securely prevented. Further, the blasting with dry ice is considered to moderate the sharpness of protrusions on the base material surface, produced by the alumina blasting, thereby reducing stress concentration that can occur at the tops of such protrusions. This also will lead to prevention of peeling of an attached film. The sublimable blasting material (e.g. dry ice) used in the second blasting is generally softer than the non-sublimable blasting material (e.g. alumina) used in the first blasting. This explains the effect of moderating the sharpness of protrusions on the base material surface without reducing the anchor effect.

Ultrasonic cleaning, for example, can be carried out in the cleaning step. In this embodiment, the metal base material 40 which has undergone the second blasting step is immersed in a cleaning liquid 42, such as pure water, and ultrasonic waves are applied to the cleaning liquid 42, thereby cleaning the metal base material 40 (see FIG. 2C).

The cleaning can almost completely remove the residual blasting particles remaining on the metal base material 40 and which can fall off. Instead of the above-described ultrasonic cleaning, it is possible to carry out in the cleaning step high-pressure water cleaning in which high-pressure water is jetted to the surface of the metal base material 40, brash cleaning in which the surface of the metal base material 40 is brushed while supplying cleaning water to the surface, etc. The cleaning step may be omitted.

As described hereinabove, according to the method of the present invention, the second blasting step using a sublimable blasting material, e.g. dry ice, is carried out after carrying out the first blasting step using a rigid non-sublimable material, e.g. alumina. This makes it possible to almost fully remove the residual non-sublimable blasting material adhering to the surface of the metal base material 40 and which is hard to remove, thereby significantly reducing the generation of particles deriving from the residual blasting material. Further, the surface of the metal base material 40, which has been properly roughened by the first blasting step, is not adversely changed (rather, may be favorably changed) by the second blasting step. Thus, due to the anchor effect produced by the roughened surface of the metal base material 40, the adhesion of an attached film to the surface increases. The generation of particles deriving from such a film can therefore be significantly reduced.

A description will now be given of experiments which were conducted to demonstrate the advantages of the method of the present invention.

The surface of the shower head 22 made of nickel as the metal base material 40 was subjected to blasting with alumina as the first blasting step, and then to blasting with dry ice as the second blasting step according to the method of the present invention. A carbon tape, having strong adhesive power, was attached to the processed surface of the shower head 22. After a short while, the tape was peeled off and the adhesive surface of the tape was observed with an electron microscope.

In Comparative Examples 1 to 3, blasting of the shower head 22 with alumina was first carried out in the same manner as in the method of the present invention. Next, in Comp. Example 1, ultrasonic cleaning was carried out three times on the surface of the shower head after the blasting. In Comp. Example 2, the surface of the shower head after the blasting was subjected to brush cleaning in which the surface was brushed while supplying a cleaning liquid to the surface. In Comp. Example 3, the surface of the shower head after the blasting was subjected to high-pressure water cleaning in which high-pressure water was jetted to the surface.

A carbon tape, having strong adhesive power, was attached to the processed surface of the shower head 22 of each of Comp. Examples 1 to 3. After a short while, the tape was peeled off and the adhesive surface of the tape was observed with an electron microscope.

FIG. 4 shows electron photomicrographs at ×50 and ×1000 magnification. There is a considerable amount of residual blasting material adhering to the tape in Comp. Examples 1 to 3, whereas only a small amount of residual blasting material adheres to the tape in the case of the shower head processed by the method of the present invention. The results thus demonstrate the effectiveness of the method of the present invention. As can be seen from the ×1000 photograph, even the residual blasting material having a particle size of not less than about 0.1 μm can be effectively removed by the method of the present invention.

The particles adhering to the carbon tape were analyzed by means of a component analyzer. The analysis revealed the presence of Al element and O element, indicating that the particles attached to the carbon tape is Al₂O₃ (alumina).

Further, an experiment was conducted in which a shower head, which had been processed by the method of the present invention or by a conventional method, was installed in a processing apparatus, the temperature of the shower head was raised, and the number of particles generated was measured. The results are shown in FIG. 5. In particular, a shower head was processed by the above-described method of Comp. Example 1 as a conventional method. Separately, the same shower head was processed by the method of the present invention as follows: the shower head was subjected to alumina blasting (first blasting) and then to dry ice blasting (second blasting), followed by ultrasonic cleaning.

Each processed shower head was installed in the film-forming apparatus described above with reference to FIG. 1. A semiconductor wafer was placed on the stage 8, and the internal temperature of the processing container 4 was raised with the heating means 10. Thereafter, the number of particles adhering to the surface of the semiconductor wafer was counted. The number of particles is shown in the table of FIG. 5. The preset temperature of the heating means 10 (corresponding to film-forming temperature) was varied as follows: 200° C., 450° C. and 640° C. The number of particles was counted also in the case where the interior surface of the processing container was subjected to pre-coating, and then the internal temperature of the processing container was raised with the heating means 10 set at 450° C.

As shown in FIG. 5, the numbers of particles at the temperatures 200° C., 450° C., 640° C. and 450° C. (with pre-coating film) of the heating means 10 are 593, 161, 687 and 62, respectively, in the case of the shower head processed by the conventional method; and 3, 39, 30 and 0, respectively, in the case of the shower head processed by the method of the present invention. This indicates that the shower head processed by the method of the present invention generates significantly decreased particles compared to the shower head processed by the conventional method. The comparative data thus demonstrates the effectiveness of the method of the present invention.

[A Variation of the Method of the Present Invention]

A variation of the method of the present invention will now be described. In the above-described embodiment blasting is carried out on the entire surface of the metal base material 40; however, the first and second blasting steps may be carried out only on a selected area of the surface of a metal base material.

FIGS. 6A and 6B are diagrams illustrating a variation of the method of the present invention. FIG. 6A is a plan view showing a portion of the gas jet surface of a shower head after blasting, and FIG. 6B is a cross-sectional view illustrating blasting of the surface portion.

In this embodiment the first and second blasting steps are selectively carried out only on a surface area around each of the gas jet holes 30 provided in the shower head 22. Thus, as shown in FIG. 6A, the first and second blasting steps are selectively carried out only on areas 44 (dotted) around the gas jet holes 30 in the gas jet surface 28 of the shower head 22. The diameter L1 of each gas jet hole 30 is, for example, about 1 mm, and the diameter L2 of each annular area 44 is, for example, about 3 mm.

Blasting of such selected areas may be carried out with the use of a mask 48, having a plurality of holes 46 of the same diameter as the areas 44, disposed in front of the shower head 22 such that each hole 46 faces each gas jet hole 30. The second blasting step, however, may be carried out without the mask 48.

Blasting of such selected areas is carried out for the following reasons: Micro irregularities, produced by blasting in the gas jet surface 28 of the shower head 22, increases the surface area. When the shower head 22 is used as an upper electrode, it is possible that the increase in the surface area may produce a considerable difference in the capacitance, formed between the upper electrode and a lower electrode, from a design value. It is nevertheless desirable to carry out blasting on those areas around the gas jet holes 30 where peeling of a film is likely to occur, thereby enhancing the adhesion of a film and preventing the peeling of the film. Thus, in such a case, blasting may be carried out only on the areas 44 around the gas jet holes 30.

Though in the above-described embodiments the processing apparatus is to form a Ti film, the present invention is also applicable to any processing apparatus for forming any other type of film. Though in the above-described embodiments the shower head 22 is configured for application of a high-frequency power thereto, the present invention can also be applied to the shower head 22 to which no high-frequency power is applied.

A processing object to be processed by the processing apparatus is not limited to a semiconductor wafer; a glass substrate, an LCD substrate, a ceramic substrate, etc. may also be processed. 

1. A surface treatment method for performing predetermined surface treatment of a metal base material, comprising: a first blasting step of carrying out blasting of the surface of the metal base material by using a non-sublimable blasting material composed of a non-sublimable material; and a second blasting step of carrying out blasting of the surface of the metal base material, which has undergone the first blasting step, by using a sublimable blasting material composed of a sublimable material.
 2. The surface treatment method according to claim 1, further comprising a cleaning step of cleaning the surface of the metal base material which has undergone the second blasting step.
 3. The surface treatment method according to claim 1, wherein the non-sublimable blasting material is a material selected from the group consisting of a ceramic material, a resin, a metal oxide and quartz.
 4. The surface treatment method according to claim 1, wherein the non-sublimable blasting material is a ceramic material selected from alumina (Al₂O₃), aluminum nitride (AlN), silicon nitride (SiN) and silicon carbide (SiC).
 5. The surface treatment method according to claim 1, wherein the non-sublimable blasting material is a metal oxide which is ZrO₂ or TiO₂.
 6. The surface treatment method according to claim 1, wherein the sublimable blasting material is dry ice.
 7. The surface treatment method according to claim 1, wherein the metal base material is a shower head for use in a processing apparatus for carrying out predetermined processing of a processing object.
 8. The surface treatment method according to claim 1, wherein the metal base material is a processing container for use in a processing apparatus for carrying out predetermined processing of a processing object.
 9. The surface treatment method according to claim 1, wherein the first and second blasting steps are carried out only on a selected area of the surface of the metal base material.
 10. The surface treatment method according to claim 9, wherein the metal base material is a shower head for use in a processing apparatus for carrying out predetermined processing of a processing object, and wherein the first and second blasting steps are carried out only on an area around each of gas jet holes provided in the shower head.
 11. A shower head which has undergone the surface treatment according to claim
 7. 12. A processing container which has undergone the surface treatment according to claim
 8. 13. A processing apparatus for performing predetermined processing of a processing object, comprising: the processing container according to claim 12; the shower head according to claim 11; a stage, for placing the processing object thereon, provided in the processing container; and an exhaust system for evacuating the atmosphere in the processing container. 